Under UMTS standards based on W-CDMA (W-Code Division Multiple Access) techniques, the downlink as well as the uplink dedicated physical channel (DPCH) is power controlled. In particular, from the user equipment (UE) point of view, it means that more or less power can be asked of the base or primary stations (BS) forming the fixed network in order to reach the Quality of Service (QoS) determined by the network itself. In the UMTS standard this QoS is measured in terms of the Block Error Rate (BLER) and refers to Outer Loop Power Control. In order to reach the expected QoS, the UE implements an algorithm, which translates the BLER requirement into a target SIR (Signal to Noise and Interference Ratio). This algorithm is frequently termed the target SIR algorithm. The 3GPP standard specification does not specify a method of defining the target SIR algorithm. It is left to individuals and/or manufacturers to set their own definitions.
One of the challenges in defining the target SIR algorithm is the fact that the target SIR may vary during communication, due to a variable propagation environment, variable required BLER, and/or possible reconfiguration of the Dedicated Physical Channel (DPCH). Once the target SIR has been calculated, the UE compares the SIR measured on a slot basis on the received DPCH with the target SIR. If the measured SIR is below the target SIR, the UE will require more power from the BS. Conversely, if the measured SIR is above the target SIR, the UE will signal the BS to decrease its transmitted power. This procedure is referred to as the Inner Loop Power Control.
Depending on the algorithm chosen for the target SIR, the performance of the receiver will be affected. In particular there are requirements in the UMTS standard specifying the maximum power a UE can ask and the maximum BLER allowed, as well as the convergence time to the required quality, for several propagation scenarios. Operators also have their own criteria in terms of maximum downlink power. Operators compare each UE to a reference UE and a UE unable to reach the desired quality at less or equal to the corresponding downlink power supplied to the reference UE may be rejected. An efficient target SIR algorithm is therefore needed.
Known proposals for open loop power control in third generation wireless communication systems are disclosed in US 20050243752 A1, EP 1067815 A1, US 20050099968 A1, WO 2005032011 A1, US 20050085255 A1 and GB 2408419 A1. US 20050243752 A1 discloses a target SIR which is adjusted based on a filtered scaling factor derived from a comparison of cell loading with a threshold. More particularly the target SIR is increased when the cell loading is high. EP 1067815 A1 discloses increasing a target SIR if the cell load is greater than a threshold. US 20050099968 A1 identifies that the synchronisation channel SCH is transmitted without being channel coded, that is scrambled, and may be regarded as a source of interference degrading the dedicated control channel DCCH if they overlap. In order to resolve this problem it is proposed that the target SIR be increased whenever the DCCH and SCH overlap. WO 2005032 011 A1 discloses setting of a target SIR based on frame errors in a dedicated physical data channel (DPDCH) and the field transmitted through the backward DPDCH. US 20050085255 A1 discloses setting a target SIR based on information from a number of channels. Finally, GB 2408419 A1 discloses setting the target SIR depending on the type of service provided.
Important points relating to setting the target SIR procedure are:                (1) The target SIR is in general a very long-term procedure requiring decoding of hundreds of blocks in order to have good BLER statistics before changing the target SIR value. This target SIR value is consequently very stable in time.        (2) The target SIR initial value is also important. Two approaches to setting this value can be found in the literature. In one of the two approaches a high value is set to ensure the decoding whatever the propagation conditions and in the other of the two approaches an average value, determined after analysis of the test cases provided in the standard, is set.        
None of these prior proposals consider open loop power control when unloaded cell conditions prevail. Unloaded cell conditions are a realistic case in the field and a common case in Inter-operability Test (IOT). The main characteristics of unloaded cells are: low interference from other users, good lor/loc (ratio between in-band received signal power and other surrounding cells interference power), SCH (Primary Synchronisation Channel (PSCH) used for slot timing and Secondary Synchronisation Channel (SSCH) used for frame synchronisation) and Primary Common Control Physical Channel (PCCPCH).